Laterally π‑Extended Dithia[6]helicenes with Heptagons: Saddle-Helix Hybrid Molecules

A laterally π-extended dithia[6]­helicene <b>1</b>, representing an interesting saddle-helix hybrid molecule containing an unusual heptagon, has been synthesized by MoCl₅-mediated oxidative stitching of tetrakis­(thienylphenyl)­naphthalene precursor <b>2</b> involving reactive-site capping by chlorination and subsequent Pd-mediated dechlorination of tetrachlorinated intermediate <b>1-Cl</b>_<b>4</b>. Highly distorted, wide helical structures of dithia[6]­helicenes (<b>1</b> and <b>1-Cl</b>_<b>4</b>) were clarified by single-crystal X-ray diffraction analyses where heterochiral slipped π–π stacking was displayed in a one-dimensional fashion. Notably, theoretical studies on the thermodynamic behavior of <b>1</b> predicted an extraordinarily high isomerization barrier of 49.7 kcal·mol^–1, which enabled optical resolution and chiroptical measurements. Electronic structures of these huge helicenes were also examined by photophysical and electrochemical measurements